secondary souring

so I have 5 gal belgian strong golden ale sitting in primary right now. I would like to pull off a gallon and give the gallon some funk. first plan of attack is to get some dreggs from a commercial bottle or two grow it in a starter for a week or two. then decant and rack beer onto it. was thinking about adding some sugars for the new bugs but dont know if the yeast will give the bugs a chance at it.

concerns: this beer is pretty high abv. it is shaping up into between 9%-10%. I dont know how much this matters but i have read IBUs have an effect. the beer is about 27 IBUs.

does my plan seem like it could work or should i just leave all five gallons together and try this with a different beer from the get go?

im thinking about starting the dreggs on some cherries in a one gallon carboy. let the culture grow for a week or two then racking the beer on top of that. Would that work?

The dreggs of your bottles, if unpasteurized, are going to likely have brewers yeast, wild yeast, and bacteria. If you toss that on fresh cherries, the brewers yeast will likely multiply while the others won't. My suggestion would be to boil some maltodextrin and/or lactose, pour that in the carboy, and rack the beer on top of that. Then toss the dreggs in on top of everything and wait 6 to 18 months. No need for a starter. If you want to do the cherries, you could add them with the maltodextrin or even after a few months.